1. Field of the Invention
This invention relates to a storage device for storage of optional data, data management information for controlling this optional data and the area management information for supervising the state of the area in which to store the data, and to a data processing system employing this storage device. The invention also relates to a data writing and readout method for writing or reading out the optional data, data management information for controlling this optional data and the area management information for supervising the state of the area in which to store the data, into or from the storage device.
2. Description of the Related Art
Up to now, a card type external storage device, referred to hereinafter as a memory card, employing a flash memory (electrically erasable programmable read-only memory (ROM)) as a recording medium, has been proposed as an external data storage device used for an electronic equipment.
In this memory card, optional data and the management information as ancillary data are stored in a memory as a storage medium. When these data and the management information are sent from the memory card to e.g., a host side computer, the data or the management information is corrected for errors, using the error correction codes, to correct the data for errors produced by cell malfunctions before outputting the data or information.
As the above management information, the information for management of the state of an area for data storage (area management information), such as the information specifying whether or not the area holding the data on memory is usable, is occasionally stored, in addition to the data-dependent information for supervising the data (data management information), such as logical addresses indicating the sequence of the stored data.
Since the area management information is the information concerning an in-memory area, that is information independent of data, there may arise the necessity of rewriting the information after storage of the data, and hence the area management information is usually adapted to be rewritten by itself without rewriting the data.
Also, if an error is produced in the area management information, and a usual error correction code is used to correct the information for errors, the error correction codes need to be rewritten every time the information is rewritten. Thus, for the area management information, the same information is desirably distributed in plural bits and stored in this state in order to combat errors without employing the error correction code for error correction.
However, if the area management information is distributed in plural bits and stored in this state, transmission data is increased in length when reading out data from the memory card, thus deteriorating the transmission efficiency. Recently, there has been proposed a technique of storing the information of plural bits in a single cell. If the number of bits stored in a cell is increased, it becomes necessary to increase the number of distributed bits for combatting errors thus further deteriorating the transmission efficiency.
Also, if the cell structure of the memory card is changed, such that the manner of information distribution is changed, it becomes necessary to change the configuration of data sent from the host side to the memory card, the structure of a driver for the host side to manage the memory of the memory card or the interface specifications need to be changed to render compatibility with the existing memory card difficult. In particular, in the case of the electronic equipment having a built-in driver, such as a digital camera, new memory cards cannot be used because software version upgrading measures cannot be used.